The present invention relates to a method for transforming image data from a higher resolution to a lower resolution.
There are some kinds of display equipment such as printers or digital copiers, which are constructed and designed to produce an image on paper or other print materials by placing dots in virtual positions referred to as pixels and defined by a digital raster.
The dots on the pixels are produced on the print material with a marking engine. The marking engine imparts clusters of energy to the surface of a display medium with, for example, a laser beam. The surface of the display medium is generally formed of material that can be charged or discharged such as photoconductive materials. The clusters of energy can discharge the positions or pixels of the charged medium surface which the laser beam scans, and a charge pattern is thus formed. The charge pattern is subsequently developed by attracting toner to it, and then transferred to the print material such as paper.
To form a complete charge pattern on the medium surface, the marking engine sequentially scans the surface following a series of scan lines in each of which the pixels lie. The laser beam scans these pixels one by one to selectively mark dots in desired pixels. After development and transference, those dot patterns are displayed on the print material to show an image as a whole. The resolution of a displayed image is defined with the number of the pixels, in each of which a dot can be marked or can be left blank, that can be displayed within a unit dimension, such as dots per inch (xe2x80x9cDPIxe2x80x9d). Higher resolution indicates smaller dot size and higher dot number per unit dimension.
In general, the resolution along the direction in which the scan lines extend can be controlled according to the minimum time interval between the laser being turned on and off, and this minimum time interval can be controlled as small as desired related to the tolerance of human eye. A shorter minimum time interval will result in a dot with smaller dimension and therefore a higher resolution along the direction in which the scan lines extend. On the other hand, the resolution along the direction perpendicular to the scan line, which depends on the number of the scan lines per unit dimension, is generally fixed and determined by the interplay between the paper moving mechanism and the laser scanning speed. This fixed one is usually referred to as the resolution of the display equipment.
Sometimes, image data is transmitted between equipment with different resolutions. For example, the image data may be transmitted from a low-resolution scanner to a high-resolution printer, or on the contrary from a high-resolution scanner to a low-resolution printer. In the latter situation, the image data, must be transformed from the original resolution to a lower target resolution to meet the performance that a terminal equipment can provide. Therefore, a method to implement this resolution transformation is required.
The present invention proposes a novel method to transform a source image into a target image with the original resolution N time to the target resolution. Firstly, the original image data of pixels is read and stored for N scan lines. This image data of original pixels is then grouped into a series of matrices each including N2 pixels having a dimension substantially coinciding with that of the target unit.
Subsequently, the matrices are classified as one of various matrix types defined previously according to the data of the original pixels in the matrix, wherein matrices with different numbers of original dots should be classified as different matrix types. Thereafter, target image is formed with a plurality of target units each determined based on respective corresponding matrix.
To form the target image, a target unit is drawn with target dots having a larger total area when its corresponding matrix includes a larger number of the original dots. A target unit is drawn with one target dot having a width no less than that of the unit itself when its corresponding matrix includes N2 original dots. A target unit is drawn with no target dot when its corresponding matrix includes no original dot.
For a preferred embodiment with N equal to 2, there can be one target dot in a target unit or two target dots respectively located at the left and right sides of the unit. For the case of one target dot, the target dot is biased to the left side when the corresponding matrix includes more original dots on the left side than on the right side. Alternatively, the target dot is biased to the right side when the corresponding matrix includes more original dots on the right side than on the left side. For the case of two target dots, the target dot at the left side is larger than the one on the right side when the corresponding matrix includes more original dots on the left side than on the right side. Alternatively, the target dot at the left side is smaller than the one on the right side when the corresponding matrix includes more original dots on the right side than on the left side.